Question

Although pure \(\mathrm{NaOH}\) and \(\mathrm{NH}_{3}\) have very different properties, their aqueous solutions possess many common properties. List some general properties of these solutions, and explain their common behavior in terms of the species present.

Short answer

Aqueous solutions of sodium hydroxide (NaOH) and ammonia (NH3) have common properties due to the presence of hydroxide ions (OH-) in both solutions, which contributes to their basic nature, conductivity, pH greater than 7, and ability to react with and neutralize acids. The dissociation of NaOH in water and the reaction of NH3 with water lead to the formation of mobile ions (Na+, OH-, NH4+, and OH-) that give these solutions their characteristic properties.

Step-by-step solution

Identify the species present in the solutions

In the aqueous solution of sodium hydroxide (NaOH), the compound dissociates completely into its constituent ions: \[NaOH_{(aq)} \rightarrow Na^+_{(aq)} + OH^-_{(aq)}\] In the aqueous solution of ammonia (NH3), it reacts with water to form ammonium ions (NH4+) and hydroxide ions (OH-): \[NH_{3(aq)} + H_2O_{(l)} \leftrightarrow NH^+_{4(aq)} + OH^-_{(aq)}\]

List their general properties

Some common properties of aqueous solutions of NaOH and NH3 are: 1. Basicity: Both solutions are basic due to the presence of hydroxide ions (OH-). 2. Conductivity: Both solutions are capable of conducting electricity because of the presence of mobile ions (Na+, OH-, NH4+, and OH-). 3. pH: Both solutions have a pH greater than 7, which is a characteristic of basic solutions. 4. Reactivity with acids: Both solutions will neutralize acids and produce water and a salt as the products.

Explain their common behavior

The behavior of NaOH and NH3 solutions is mainly due to the presence of hydroxide ions (OH-) in both solutions. Hydroxide ions are responsible for the basic properties of these solutions, such as the capability to neutralize acids and increase the pH of the overall solution. The presence of mobile ions, Na+, OH-, and NH4+, contributes to their conductivity.

Key concepts

Basicity of Solutions

When discussing the basicity of solutions, we are mainly interested in the presence of hydroxide ions (OH^-). These ions are key contributors to the basic (or alkaline) nature of aqueous solutions. In the case of an aqueous sodium hydroxide (NaOH) solution, the compound dissociates to release Na^+ ions and OH^- ions into the solution. In a similar manner, ammonia (NH_3) reacts with water to produce ammonium (NH_4^+) and hydroxide ions.

Both NaOH and NH_3 solutions share a common basic character due to the hydroxide ions. The more of these OH^- ions are present, the stronger the basicity of the solution. This basicity can be measured on a scale known as the pH scale, with higher concentrations of hydroxide ions resulting in a higher (more basic) pH value.
Why is this important? Understanding basicity helps with predicting the outcome of many chemical reactions, especially those involving acids and bases.

Electrical Conductivity

The electrical conductivity of an aqueous solution is a measure of how well it can conduct electricity, which is directly influenced by the presence of ions. Ions are charged particles that, when free to move, carry electric current.

Consider our examples, the aqueous solutions of NaOH and NH_3. In the case of NaOH, it fully dissociates into sodium (Na^+) and hydroxide (OH^-) ions. This results in a high concentration of ions that can move freely and thus, conduct electricity effectively. NH_3, on the other hand, forms ammonium (NH_4^+) and hydroxide ions upon reacting with water. As a result, NH_3 solutions also have a good electrical conductivity.
Electrical conductivity is especially significant in industries and research where the ion content of a solution must be monitored or controlled, like in water purification or battery technology.

pH Level

• pH is a scale used to specify how acidic or basic a water-based solution is.
• pH levels range from 0 to 14, with 7 being neutral, values less than 7 indicating acidity, and greater than 7 indicating basicity.

Both the NaOH and NH_3 solutions have pH levels above 7, meaning they are basic. The OH^- ions are responsible for the increase in pH as they reduce the concentration of hydrogen ions (H^+) in the solution through the formation of water (H_2O).

Monitoring pH is critical in fields like agriculture, medicine, and environmental science. For instance, the human body's pH level is tightly regulated; slight deviations can significantly affect health. Similarly, soil pH can influence plant growth, affecting agricultural productivity.

Acid-Base Neutralization

Acid-base neutralization is a chemical reaction where an acid and a base react to form water and a salt. In our examples, both NaOH and NH_3 can neutralize an acid. This is because they contain OH^- ions that combine with H^+ ions from the acid to produce water. Moreover, the remaining parts of the dissociated acid and base typically combine to form a salt.

Understanding neutralization reactions is crucial for various applications like antacid medications that neutralize stomach acid, or in analytical chemistry, where titration is used to determine unknown concentrations of acids or bases. These reactions are also fundamental to processes in biological systems and environmental management.